1. Field of the Invention
The invention relates to a new type of low temperature bleaching system and a method for cleaning substrates therewith.
2. The Related Art
Many household and personal care products are formulated with an active oxygen-releasing material to effect removal of stain and soil. Oxygen-releasing materials have an important limitation; their activity is extremely temperature dependent. Temperatures in excess of 60.degree. C. are normally required to achieve any bleach effectiveness in an aqueous wash system. Especially for cleaning fabrics, high temperature operation is both economically and practically disadvantageous.
The art has partially solved the aforementioned problem through the use of activators. These activators, also known as bleach precursors, often appear in the form of carboxylic acid esters or amides. In an aqueous liquor, anions of hydrogen peroxide react with the ester or amide to generate a corresponding peroxyacid which oxidizes the stained substrate. Commercial application of this technology is found in certain fabric bleaching detergent powders incorporating tetraacetylethylenediamine (TAED) and sodium nonanoyloxybenzene sulfonate (SNOBS).
TAED is effective only under warm-hot wash conditions, i.e. above 30.degree. C. Although this material is widely employed in Europe with laundry detergent, cold water consumer washing habits have not permitted use in the United States. SNOBS can operate at lower temperatures than TAED. For this reason it has been commercialized in the United States but its performance could still be improved.
Another problem with carboxylic acid ester or amide bleach precursors such as TAED and SNOBS is that conversion to peracid is inefficient. A further difficulty is that they are not catalytic. Once the ester or amide has been perhydrolyzed it can no longer be recycled. Accordingly, relatively large amounts of precursor are necessary. Amounts as high as 8% may be necessary in a detergent formulation for bleaching fabrics. Cost for these relatively expensive chemicals is of major concern at such high use levels.
Outside the context of consumer products, there have been reports of catalytic oxidizing agents. F. A. Davis and coworkers, in a series of articles, reported preparation of a new class of stable oxidizing agents, namely 2-arenesulfonyl-3-aryl-oxaziridines. See Davis, Nadir, and Kluger, J.C.S. Chem. Comm. 1977, 25; Davis, Lamendola Jr., Nadir, Kluger, Sederjarn, Panunto, Billmers, Jenkins Jr., Turchi, Watson, Chen and Kimura, J. Amer. Chem. Soc. 1980, 102, 2000; and Davis, Chattopadhay, Towson, Lal and Reedy, J. Org. Chem. 1988, 53, 2087. These oxaziridines were prepared by peracid or monopersulfate oxidation of a corresponding sulfonimine under alkaline conditions. In late 1988, Davis published a paper entitled "Selective Catalytic Oxidation of Sulfides to Sulfoxides Using N-sulfonyloxaziridines", J. Org. Chem. 1988, 53, 5004. Therein described is a system where sulfonimine reacts with monopersulfate to generate an in situ oxaziridine in a toluene-water biphasic mixture. Oxaziridine then coverts the sulfide to a sulfoxide and generates starting sulfonimine, thereby rendering the process catalytic in nature. Beyond use as a synthetic tool, there is no suggestion of any possible application for sulfonimine chemistry to the problem of removing stain in consumer applications, such as in cleaning fabrics.
It is an object of the present invention to provide an improved bleaching system and detergent composition containing such system that operates over a wide temperature range including that of under 60.degree. C.
It is another object of the present invention to improve the performance of bleach precursors that normally would be inoperative under low temperature wash conditions.
A further object of the present invention to provide bleach improvement through catalysts effective in relatively small amounts so as to avoid any substantial incremental costs.
A still further object of the present invention is to provide a method for bleaching stained substrates such as clothes, household hard surfaces including sinks, toilets and the like, and even dentures.
Other objects of the present invention will become apparent through the following summary, detailed discussion and examples.